Also Shingoshi, most cryogenic coolers are designed to bring something down to temperature and then just keep it there, heavily insulated. For what we use, it becomes alot harder as were pumping a hell of a lot of energy into the system. A very auto cascade could run extremely low temperatures if it wasnt expected to cope with any sort of load. There is a thread somewhere on here (good luck finding it) either wrdzal or chilly1 showed what an auto-c could accomplish without any load holding capabilities, i think they got down to -140ish with one compressor.